Antibiotic Resistome Changes Associated with Different Types of Corrosion Inhibitors when Chlorine is used as a Disinfectant

Antibiotic resistance is a global public health issue. Efforts to understand sources that can be controlled are underway to help mitigate and slow the spread. Drinking water distribution systems contain stressors that can promote antibiotic resistance including chlorine and metals. Corrosion inhibitors are required to prevent the leaching of metals into drinking water. While utilities have a choice of which corrosion inhibitor they employ, the impact of corrosion inhibitor type when combined with chlorine on antibiotic resistance is unknown. The objective of this research was to understand the impacts of zinc orthophosphate, sodium orthophosphate, and sodium silicate, three commonly used corrosion inhibitors, on antibiotic resistance when mixed with chlorine. Culture based plating was paired with metagenomics analysis on lab-scale microcosms. The addition of all three corrosion inhibitors resulted in a significantly higher absolute abundance of antibiotic resistant bacteria with resistance to rifampicin, sulfamethoxazole, and vancomycin, while the addition of phosphate-based inhibitors (sodium orthophosphate and zinc orthophosphate) at 1 mg/L also resulted in significantly higher absolute abundance of ampicillin-resistant bacteria. Exposure to all three types of corrosion inhibitors and free chlorine led to significantly higher abundances of ARGs conferring resistance to the target antibiotics used in the phenotypic assessment. In addition, observed changes in the resistomes compared to the controls were influenced by an enrichment in ARGs responsible for multidrug resistance and resistance to peptide antibiotics. In general, most of the ARGs were associated with chromosomes (non-MGE), but a significant increase in the number of ARGs co-located with plasmid and integron sequences was observed. In contrast, the abundance of viral-associated ARGs decreased in the treatments compared to the controls. These results highlight the importance of corrosion inhibitor selection and the potential impacts on the abundance and distribution of ARB, ARG, and MGEs in potable water systems.